Junction field effect transistors (JFETs) are commonly used in power transistor and switching applications such as power supplies, power converters, energy systems, telecommunications, motor control, automotive, and consumer electronics. Power devices generally refer to transistors and other semiconductor devices that can switch about 1.0 ampere or more of conduction current. Power JFETs are well known as high input impedance, voltage controlled devices, which require only a small charge to initiate turn-on from relatively simple drive circuitry. Ideally, power JFETs should exhibit high drain to source current carrying capacity, low drain to source resistance (RDSon) to reduce conduction losses, high switching rate with low switching losses, and high safe operating range (SOA) which provides the ability to withstand a combination of high voltage and high current.
Most if not all known power JFETs have a relatively thick drift or epitaxial (epi) region for high voltage isolation in the depletion layer, i.e., for a high breakdown voltage. The epi region also has a relatively low doping concentration. The combination of relatively thick epi and low doping concentration tends to increase the RDSon of the JFET. The higher the voltage application, the thicker the epi region needed for isolation. The thicker the epi region, the higher the RDSon. A higher RDSon increases the switching losses and decreases the efficiency of the JFET in high voltage power switching applications. The relationship between thick epi for high voltage isolation and high RDSon may impose practical limitations of about 60 volts for high voltage applications using known JFET devices.
A need exists for JFETs with lower drain-source resistance for use in high voltage applications.